Air core reactors are inductive devices used in high voltage power transmission, distribution and industrial applications. Air core reactors are used for a variety of purposes, including for filtering out harmonics, as shunt devices which compensate for introduction of capacitive reactive power, and as devices which limit short circuit currents. Air core reactors are formed with a series of concentrically positioned, spaced-apart winding layers, referred to as packages, in a cylindrical configuration. The packages are positioned between upper and lower current carrying members, sometimes referred to as spider units or spiders. The spider units include a plurality of arms radiating along a plane and away from a central hub position in a star configuration. Among other functions, the spider units may serve as terminals for connecting power lines and for interconnecting the winding layers in an electrically parallel configuration. The reactors are normally installed with the spider units in a horizontal orientation with respect to an underlying horizontal ground plane so that the major axis of the cylindrical configuration extends vertically upward from the ground plane. For a single reactor, or for the lower-most reactor in a stacked configuration of two or more reactors, the winding layers are supported above the ground by the lower spider unit and a series of insulators and structural leg members which extend from the lower spider unit to the ground.
Because air core reactors carry alternating current through coiled electrical conductors, they are subjected to mechanical forces created by the interaction of the electrical current and the magnetic field generated by the reactor. FIG. 1 illustrates the general direction of net forces exerted on a typical air core reactor 1 during power operation. Due to the design of the device, the frequency of the force is twice the frequency of the current, and the magnitude of the force is proportional to the square of the current. Due to the relative flexibility of the cylindrically shaped packages in the horizontal direction, the side surfaces of the reactor tend to vibrate in response to the forces, thereby creating audible sound.
Air core reactors are often located in populous areas, and the sound created by the reactors can be a serious irritant to the local population. It is known to locate air core reactors behind walls to isolate them, or to construct a separate sound shield around each reactor to surround it with sound absorbing material. The cost of such structures is high, and they may inhibit physical access to the reactor for maintenance activities.